In recent years, along with the upsizing of liquid crystal televisions, a backlight chassis of the liquid crystal television has been upsized as well. The backlight chassis refers to a member which is disposed on the back side of a backlight for the liquid crystal television and which holds a liquid crystal panel and the above-described backlight from the back. The backlight chassis is required to have rigidity to support a light, flatness to avoid contacting the light against a liquid crystal portion, cracking, or the like, and no feeling of oil canning In addition, a reduction in thickness is desired for the purpose of slimming the television and a reduction in raw material cost.
However, along with the above-described upsizing and reduction in thickness of the backlight chassis, problems related to the rigidity and flatness have appeared. It is believed that formation of a bead by subjecting a flat plate surface of the above-described backlight chassis to stretch forming is effective to ensure the above-described rigidity. It was found, however, that working of the flat plate surface caused new problems, such as degradation in flatness and an increase in feeling of oil canning. The above-described degradation in flatness of the backlight chassis and the like are phenomena which occur because of poor shape fixability in pressure forming. Consequently, a steel sheet used for the backlight chassis has been required to have workability and, in addition, has been required to have shape fixability. Regarding the steel sheet which has been used previously, however, there is a problem in that the workability is provided to a certain extent, but sufficient shape fixability cannot be provided.
Examples of steel sheets provided with the above-described shape fixability include a steel sheet produced by a method in which the amount of spring back in bending is reduced by controlling aggregation texture and, in addition, specifying at least one of r values in the rolling direction and the direction perpendicular to the rolling direction to be 0.7 or less, as disclosed in, for example, Japanese Patent No. 3532138. In addition, a steel sheet in which spring back and wall camber in bending are suppressed by controlling the anisotropy of local elongation and uniform elongation, as disclosed in Japanese Unexamined Patent Application Publication No. 2004-183057, is included. Furthermore, a ferrite based thin steel sheet, in which spring back in bending can be suppressed by specifying the X-ray diffraction intensity ratio of the {100} face to the {111} face to be 1.0 or more, as disclosed in International Patent Publication No. WO 2000/6791, is included.
Each of the steel sheets of JP '138, JP '057 and WO '791 has the shape fixability in bending to a certain extent. However, there is a problem in that sufficient shape fixability is not obtained in the case of working, for example, stretch forming, where high ductility is required. Moreover, there is a problem in that the shape fixability is enhanced, but the rigidity and the workability of the steel sheet are degraded.
It could therefore be helpful to provide specified components and r values and, thereby, provide a cold-rolled steel sheet provided with excellent workability and shape fixability, a method for manufacturing the same, and a backlight chassis.